Chapter 11: Micronutrients in Metabolism
11.7 Folate (Vitamin B9)
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program
Folate
Folate is a required coenzyme for the synthesis of the amino acid methionine, and for making RNA and DNA. Therefore, rapidly dividing cells are most affected by folate deficiency. Red blood cells, white blood cells, and platelets are continuously being synthesized in the bone marrow from dividing stem cells. When folate is deficient, cells cannot divide normally A consequence of folate deficiency is macrocytic or megaloblastic anemia. Macrocytic and megaloblastic mean “big cell,” and anemia refers to fewer red blood cells or red blood cells containing less hemoglobin. Macrocytic anemia is characterized by larger and fewer red blood cells. It is caused by red blood cells being unable to produce DNA and RNA fast enough—cells grow but do not divide, making them large in size. (Figure 11.71 “Folate and the Formation of Macrocytic Anemia”)
Folate is especially essential for the growth and specialization of cells of the central nervous system. Children whose mothers were folate-deficient during pregnancy have a higher risk of neural-tube birth defects. Folate deficiency is causally linked to the development of spina bifida, a neural-tube defect that occurs when the spine does not completely enclose the spinal cord. Spina bifida can lead to many physical and mental disabilities (Figure 11.72 “Spina Bifida in Infants” ). Observational studies show that the prevalence of neural-tube defects was decreased after the fortification of enriched cereal grain products with folate in 1996 in the United States (and 1998 in Canada) compared to before grain products were fortified with folate.
Additionally, results of clinical trials have demonstrated that neural-tube defects are significantly decreased in the offspring of mothers who began taking folate supplements one month prior to becoming pregnant and throughout the pregnancy. In response to the scientific evidence, the Food and Nutrition Board of the Institute of Medicine (IOM) raised the RDA for folate to 600 micrograms per day for pregnant women. Some were concerned that higher folate intakes may cause colon cancer, however scientific studies refute this hypothesis.
Dietary Reference Intakes
The RDAs and ULs for different age groups for folate are listed in Table 11.71 “Dietary Reference Intakes for Folate”. Folate is a compound that is found naturally in foods. Folic acid however is the chemical structure form that is used in dietary supplements as well as enriched foods such as grains. The FNB has developed dietary folate equivalents (DFE) to reflect the fact that folic acid is more bioavailable and easily absorbed than folate found in food. The conversions for the different forms are listed below.
1 mcg DFE = 1 mcg food folate
1mcg DFE = 0.6 mcg folic acid from fortified foods or dietary supplements consumed with foods
1 mcg DFE = 0.5 mcg folic acid from dietary supplements taken on an empty stomach
Table 11.71 Dietary Reference Intakes for Folate[1]
Age Group | RDA Males and Females mcg DFE/day | UL |
Infants (0–6 months) | 65* | Not possible to determine |
Infants (7–12 months) | 80* | Not possible to determine |
Children (1–3 years) | 150 | 300 |
Children (4–8 years) | 200 | 400 |
Children (9–13 years) | 300 | 600 |
Adolescents (14–18 years) | 400 | 800 |
Adults (> 19 years) | 400 | 1000 |
Pregnancy | 600 | Same as non-pregnant |
Lactation | 500 | Same as non-lactating |
*denotes Adequate Intake |
Dietary Sources
Folate is found naturally in a wide variety of food especially in dark leafy vegetables, fruits, and animal products. The U.S. Food and Drug Administration (FDA) began requiring manufacturers to fortify enriched breads, cereals, flours, and cornmeal to increase the consumption of folate in the American diet. For the folate content of various foods, see Table 11.72 “Folate Content of Various Foods”.
Table 11.72 Folate Content of Various Foods[2]
Food | Serving | Folate (mcg DFE) | Percent Daily Value |
Beef Liver | 3 oz. | 215 | 54 |
Fortified breakfast cereals | ¾ c. | 400 | 100 |
Spinach | ½ c. | 131 | 33 |
White rice, enriched | ½ c. | 90 | 23 |
Asparagus | 4 spears | 85 | 20 |
White bread, enriched | 1 slice | 43 | 11 |
Broccoli | 2 spears | 45 | 10 |
Avocado | ½ c. | 59 | 15 |
Orange juice | 6 oz. | 35 | 9 |
Egg | 1 large | 22 | 6 |
- Dietary Supplement Fact Sheet: Folate. National Institute of Health, Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Updated November 30, 2022. Accessed August 2, 2023. ↵
- Ibid. ↵
Megaloblastic anemia is characterized by very large, abnormal red blood cells. This is usually due to a lack of due to a lack of folate or vitamin B12.
Pregnancy is the development of a zygote into an embryo and then into a fetus in preparation for childbirth.
Fortification is adding new nutrients to enhance a food’s nutritive value. For example, folic acid is typically added to cereals and grain products, while calcium is added to some orange juice.
The Federal Food, Drug, and Cosmetic Act of 1938 gives the FDA authority over food ingredients. The FDA enforces the safety of domestic and imported foods. It also monitors supplements, food labels, claims that corporations make about the benefits of products, and pharmaceutical drugs. Sometimes, the FDA must recall contaminated foods and remove them from the market to protect public health.